I wonder if Hidan's jutsu is reliant on the amount of pain the victim feels. Every other time we've seen Hidan, he is usually out of breath in the middle of his circle. This time he was enjoying every second of the reversion back to his previous state. He was also able to stand and seemed like he was ready to conduct another ritual. When they were first introduced they fought the two tailed jinchuriki and she seemed berserk by the time they got serious. The next victim was the monk whom im sure must've had a high threshold for pain. Onr the jutsu might have a limit to the amount of pain the victim can stand. Maybe when the victim is at the maxium amount of pain they can take the jutsu wears off. Then Kakuzu probably comes in and cleans up the leftovers, which might explain the carnage surrounding the ritual.